1. Field of the Invention
The present invention relates to an optical packet switching system in which packet-by-packet optical packet switching is enabled and to an optical packet transmitter device used in the optical packet switching system.
2. Description of the Related Art
The technology of switching the path depending on the wavelength in an optical transmission system based on wavelength division multiplexing (WDM) and by employing a wavelength selective switch (WSS) is in practical use. One of the next-generation technologies studied is an optical packet switching system in which the path is switched in smaller units, namely, IP packets (10 Gigabit Ethernet (registered trademark) signals, etc.). Each packet is converted in format into an optical packet and routed by using an ultrahigh-speed optical switch (see e.g., patent document No. 1).
When the transmission is based on IP packets, no significant information is transmitted absent any data so that the bandwidth is wasted accordingly. If the optical packet switching system is realized, however, any idle time in which data is absent can be occupied by another packet. Therefore, the optical packet switching system promises the possibility of dramatically increasing the bandwidth usage efficiency of the transmission path and is envisaged as a technology of the future.    [patent document No. 1] JP 2008-235986
In the optical packet switching system, there is a need to secure gap time between optical packets commensurate with time required for the switching of optical packet signals.
FIG. 1 shows the gap time between optical packet signals. FIG. 1 shows a client signal, optical packet signals at wavelengths λ1-λ10 produced by causing the client signal to branch, and how the optical packet switching device is turned on or off. In FIG. 1, “PA” denotes a preamble and “IFG” denotes an inter-frame gap.
Referring to FIG. 1, optical packet signals are output at time intervals commensurate with the duration of the Ether frame of the client signal. As shown in FIG. 1, time required for switching in the optical packet switching device is secured and optical packet signals can be properly routed, by providing gap time between optical packet signals.
In addition to the client signal, an optical packet signal includes optical routing information, etc. For this reason, the length of an optical packet signal is not 1/N the frame length of the client signal even if the client signal is wavelength-divided by N (N is an integer equal to or greater than 2). The length of an optical packet signal is longer than 1/N the frame length. As the length of an optical packet signal at each wavelength grows larger than the length of a client signal, the gap time will be reduced with the result that sufficient time cannot be secured for switching. FIG. 2 shows how an optical packet signal is discarded because of failure to secure sufficient time for optical switching.